J_h

Purchased a C43 sedan, 2017 at 178000km. The vehicle seems really good and healthy compared to the kilometers, however I'm a bit worried about one particular noise from the engine.

After cold start when the rpm drops to the normal idle level, I can hear a knocking sound that quite distinctly comes from the left bank of the engine (viewed from the front of the car). It's very noticeable when listening with a screwdriver and connecting it to the left valve cover. It's so powerful that it almost hurts my ear when I listen through the screwdriver and I can also feel a sharp impulse in my fingers. What bothers me the most is that the right bank seems pretty much silent in this regard (also no feedback to the fingers there). Of course both of the banks have that typical healthy timing chain whirring sound, but on the left bank there is also the knocking that is clearly a separate noise.

I can't hear any timing chain slap when cold starting the engine. To me that knocking rather sounds like a valve thing. What do you think?

From the cabin I can hear something that I think is the same noise, but becomes more muted obviously. So the idle sounds like sort of deep and soft knocking from inside the car too. I can't hear the noise when I rev the engine even a tiny bit. Just to be clear, AC is turned off so it's not that. Also this is not a purge valve, I know how it sounds like and it's located in a totally different side of the engine.

The noise fades a lot when the engine warms up but is not completely silent.

Better when listened with a decent headphones:
https://www.dropbox.com/scl/fi/gyn7n...=wvplk8uq&dl=0

Also found these from Youtube, sounds pretty much or exactly like these two:

trigital

Valve or ....piston.

W205C43PFL

Those are C 300 with the M274 that sounded like the wrist pin if I recalled correctly, a non issue on the M276. Not sure why but I couldn't hear what you are talking about in the dropbox link. Could you also upload to youtube?

J_h

Sounds pretty much exactly like those c300. I don't think youtube makes any difference. I had this issue with my friend too, he didn't hear it and it seems to depend on the device you're listening on, but his headphones were absolute crap. I can hear it on my phone, monitor speakers and headphones though..

Here I tried to isolate the noise with a video editing software and now it's pretty obvious at least if you know what to listen. Now the sound breaks and sounds kind of high pitched at times because the phone mic can't handle it (my phone was basically touching the screwdriver head).

https://www.dropbox.com/scl/fi/ol1qi...=dlakphaf&dl=0

W205C43PFL

Sorry about that, maybe I have bad ears.
See if this is similar to your sound : https://mbworld.org/forums/e-class-w...76-engine.html

W205C43PFL

If you need further assistance, forum member CaliBenzDriver is the M276 expert and he will be more than happy to help you : )

J_h

This indeed sounds very similar. I mean the deeper clap on the background, not the injector tick that is normal.

W205C43PFL

I see. Hopefully you find your answer there : )

W205C43PFL

Forum member CaliBenzDriver calls it a tapping sound.

J_h

Yeah it seems like the whole discussion turned into oil viscosity but the tap tap tap noise never got explained further.

Seems like there is the water pump attached to the left cylinder bank side (mostly) so I might want to suspect that too. But it's a bit more tricky to listen to..

W205C43PFL

He did mention it could be belt related apparently

J_h

The belt area seems impossible to listen with the screwdriver method, it's so packed. But I listened from the rear end of the valve cover and the noise is loud there, perhaps even louder than from the chain side. Something tells me it's not the pulleys.

New video:
https://www.dropbox.com/scl/fi/g19u8...=ul9tutzh&dl=0

W205C43PFL

I see, let me see if I can hear this one.

W205C43PFL

OP, I finally hear what you are talking about. I will need to compare the sound next time I drive my vehicle in a week. In the meantime, hopefully someone chimes in soon.